Problem: If $a + b = 8$ and $x + y = -5$, what is $-5a - 5b - y - x$ ?
Solution: $= -5a - 5b - x - y$ $= (-5) \cdot (a + b) + (-1) \cdot (x + y)$ $= (-5) \cdot (8) + (-1) \cdot (-5)$ $= -40 + 5$ $= -35$